Steps in cohort study

PREVENTIVE MEDICINE

1. 01/09/2015 COMMUNITY MEDICINE SEMINAR 1 STEPS IN COHORT STUDY

2. CONTENTS 01/09/2015 COMMUNITY MEDICINE SEMINAR 2 Introduction What is a cohort? Elements of a cohort study Selection of study subjects Obtaining data on exposure Selection of comparison groups Follow up Analysis References

3. INTRODUCTION 01/09/2015 COMMUNITY MEDICINE SEMINAR 3 Cohort study is a type of analytical study Done to support or refute the existence of an association between suspected cause and disease Prospective / longitudinal /incidence / forward looking study CAUSE → EFFECT Types-Prospective, Retrospective, Combination

4. 01/09/2015 COMMUNITY MEDICINE SEMINAR 4

5. WHAT IS A COHORT ??? 01/09/2015 COMMUNITY MEDICINE SEMINAR 5 COHORT-a group of people who share a common characteristic or experience within a defined time period. STUDY AND CONTROL COHORTS Both should be free of disease, equally susceptible to the disease, and both groups should be comparable to each other.

6. FRAMEWORK OF COHORT STUDY 01/09/2015 COMMUNITY MEDICINE SEMINAR 6

7. ELEMENTS OF A COHORT 01/09/2015 COMMUNITY MEDICINE SEMINAR 7 1.Selection of study subjects 2.Obtaining data on exposure 3.Selection of a comparison group 4.Follow up 5.Analysis

8. SELECTION OF STUDY SUBJECTS 01/09/2015 COMMUNITY MEDICINE SEMINAR 8 General population- If exposure is frequent, an appropriate sample size(exposed and unexposed) is taken from general population. Special groups - - like selected profession, college alumini , antenatal women, etc. -exposure groups-if exposure is rare, select a cohort of persons known to have had exposure.

9. OBTAINING DATA ON EXPOSURE 01/09/2015 COMMUNITY MEDICINE SEMINAR 9 To know whether they are exposed or not, and also the degree of exposure. Various methods used are: Directly from cohort members Review of records Medical examination or special tests Environmental surveys

10. SELECTION OF COMPARISON GROUPS 01/09/2015 COMMUNITY MEDICINE SEMINAR 10 Internal comparisons- several sub groups based on level of exposure External comparisons- like smokers and non smokers Comparison with general population rates-if it is available

11. FOLLOW-UP 01/09/2015 COMMUNITY MEDICINE SEMINAR 11 Regular follow up of all participants to obtain data for assessing the outcome. F ew methods are- Periodic medical examination Review records Routine surveillance of death records Mailed questionnaires , telephone calls, home visits.

12. ANALYSIS 01/09/2015 COMMUNITY MEDICINE SEMINAR 12 Whether any association exists between the suspected factor and the disease under study If so, what is the strength of association COHORT DISEASE + DISEASE - TOTAL EXPOSED a b a+b NOT EXPOSED c d c+d

13. INTERPRETATION 01/09/2015 COMMUNITY MEDICINE SEMINAR 13  

14. REFERENCE 01/09/2015 COMMUNITY MEDICINE SEMINAR 14 Park’s Textbook of PREVENTIVE AND SOCIAL MEDICINE, 23 rd edition Textbook of community medicine by AH.SURYAKANTHA, 3 rd edition

15. Thank you 01/09/2015 COMMUNITY MEDICINE SEMINAR 15